Engine out outlanding

[Jeromef 76]

Hello all

My plane is a '95 MKIV with the twin fuel tanks option.

Yesterday, coming back from a 100mi roundtrip, at 5 min from my home airfield, my motor gasped three times and stopped. The outlanding in a large harvested wheat field was uneventful.

After landing, I found that the fuel line and fuel feeder were empty, although I supposed having at least 15l of fuel remaining. Looking further, I saw that the right tank was empty, but the left one contained still about 15l.

After adding 10l in the right tank, the engine was restarted and I could return safely to my home field.

Both tanks are connected simply by a Y fitting without a selector. It seems that when one of the tanks is empty, the pump sucks air in and the fuel feeder and fuel line become empty, leading to engine stop.

I am glad this happened over an open field!

Is that a known problem?

[wypaul 448]

Do you have the header tank installed behind the seat or are the wing tanks connected to the pump via the  Y fitting?

[Yamma-Fox 403]

Glad you had a good landing option in that field!   Nice job getting your plane down safe!! 

I think your big question is why you couldn't use the fuel in that left tank.  The guys here will have better ideas on that than I do, but my first thought is the same as "wypaul", whether or not you are equipped with a header tank.  The other thing I've seen is a failure to get ram air pressure in a tank (clogged fuel cap pressure tube / bad fuel cap gasket / fuel cap backwards)

In hopes of having a warning if a fuel feed problem arises, I  installed a low fuel warning above my 1.5 gall header tank.

This is the system Kitfox sells as an "add on" low fuel warning.  Designed to give 10-15 min warning if fuel stops flowing (empty tank - clogged finger strainer - vapor lock - etc.)

In theory a system like that should warn in a situation like you describe.

Edited 13 Aug 2018 by Yamma-Fox

[1avidflyer 1983]

To each his own, but I like having a valve for each tank, and I only run on one at a time.  I do have the ram air tubes on both gas caps as well, plus the standard Avid aluminum pipe header tank.  I think the low fuel warning is a good idea, although I don't have one.  JImChuk

[FredStork 453]

Hi Jerome,

glad you had a safe landing. There is a long string on tanks, connections and vents mith opinions, experiences, pros and cons that you might want to read. I have some ideas about what could have been your issue but would need more details. http://www.avidfoxflyers.com/index.php?/topic/5597-engine-failure-yesterday/

regards

Fred

[Jeromef 76]

In fact, I have the standard Avid header tank installed (I named it "feeder" in my original post), and ram air tubes on both sides. This header tank is installed on the right side, so the tube length to the right tank is shorter than to the left one. I already noticed that the right tank empties a bit faster tan the left one, but I wrongly supposed that normal flow would continue with one tank empty.

By the way, being a looong time glider pilot, outlanding is quite a common event for me!

[FredStork 453]

Jerome,

with the 2 tanks connected through a "Y" the 2 tanks should under normal conditions contain fule to the same level. This is most liekly the situation when yountake the plane out of the hangar. Your problem is that fuel flows easier from the left tank than from the right. In flight you see this as a difference in fuel level between the tanks. But if you land and wait a while they will get to the same level again, right?

Once one tank is empty it is apparently easier to fill the feedertank with air trough the (left) empty tank or through the vent lione of the feedertank. 2 possibilities, either the outlet, fuel line or eventual filer between the left tank and the feeder tank is partially clogged and therefore slowing the flow or the venbt on the tank is not working as expected. You say "ram air tubes", I assume this to be the classic forward facing tube sticking up into the air flow over the wing. Verify that the vent is not obstructed and if that is not the case modify the position and or length on the tube.

I recomend installing a fuel warning system in the feedertank and a switch between the left and right tank. But note that this will not resolve your issue, you need to find out why the fuel is flowing too slowly.

Now we get into the controverial part of the discussion... I recomend closing the vent line on the feedertank. It should be opened only to let air out once the level in the feedertank has gone below the alarm level, then switch tank, open the vent until the alarm stops, i.e. the feedertank is again full of fuel. 
The reason for this is, as mentionned below and in the other string, that with an obstructed, or partially obstructed, fuel line it will be easier for the fuel pump to suck ion air through the vent (or empty tank) than sucking fuel through an even just partially obstructed line. I.e. the danger of open vent lines (other than on the main tanks...) is that while thye are there to let air out they can just as well let air in. It is better to manually controll the air out.

And yes, glider pilots, as well as hang and paraglider pilots, have the advantage of always knowing where to land. Saved me when I lost my old 532 in flight...

Regards

Fred

[Yamma-Fox 403]

To each his own, but I like having a valve for each tank, and I only run on one at a time.  I do have the ram air tubes on both gas caps as well, plus the standard Avid aluminum pipe header tank.  I think the low fuel warning is a good idea, although I don't have one.  JImChuk

Jim what type of valves are you using?

I think I'd like to run them as well, for several reasons imcluding a fuel leak scenario and I will also be able to test - check my fuel level low system easier.

[1avidflyer 1983]

Real hi tech valves for me...  the snowmobile style ones like Avid supplied with their kits originally.  Look on page 18 of this LEAF catalog.  JImChuk

onlinecatalog.leadingedgeairfoils.com/18/
 

[Jeromef 76]

Fred

I did read the whole thread about the similar case that happened to Gfry.

I think that having the header vent closed or open should not make a big difference in a twin tanks system once one of the tanks is empty- because the empty tank gives a direct access to external air in the header tank? (or worse with a forward facing tank vent on the cap will feed air with a positive pressure in the line!)

By the way, sorry for the trouble with your bird. Hope the repair is in good way!

[FredStork 453]

Jerome, you are probably right, you had 2 possible ways to get air in the tank and yes the ram air in the empty tank might have blocked the flow and air could either get in ther or throught the vent or both... So separate valves for each of the tanks is good idea (it also helps to use only one tank and preserve the other one from eventual ethanol contamination).

Good luck and fixing the issue and thank you for your consideration. Repair is progressing and I should be flying by end of the month.

Fred

[Jeromef 76]

Fred

In your own MK IV, do you have the 2 tanks installed?

[FredStork 453]

Fred

In your own MK IV, do you have the 2 tanks installed?

yes I have 2 wing tanks with separate valves and a feedertank with a normally closed vent (only opened to purge air after switching tank after level alert...) 

[ChrisBolkan 130]

If you have both fuel tanks feeding a single header tank I do not believe you need a separate header vent. The header will vent to whatever tank is not supplying fuel. Is my thinking fatally flawed? This is how my Fat Avid is set up and works fine. Once all the air works its way out of the header it stays out, and both tanks feed it at the same time unless I shut one off because I am parked on an incline.

[Jeromef 76]

Chris

If both tank contain fuel, I think that without a vent there is no way for air trapped in the header tank to escape.

And yes both tanks feed the header at the same time, but not at the same rate as the circuit is not symmetrical. As I have the habit to fill the same quantity of fuel in each tank, I suppose that over time the level of fuel in the left tank has become higher that in the right one. (I use a FC10 fuel computer to estimate the remaining fuel, as checking the level in the transparent tubes inside the cabin is highly imprecise)

[ChrisBolkan 130]

Trapped air escapes the header because of the not perfectly even draw, and because any change from level flight moves fuel (and air) between the fuel tanks via the header, so air very quickly escapes the header tank to the fuel tanks and does not return. 

[Yamma-Fox 403]

Being in the "vented tank" camp, I really do not want to bring us back to an old debate, but FWIW my old KF2 (with a big "header tank" LOL) would get an airlock in the feed line  from the wing tank to the main "header" tank.

I would draw the main tank down to about half then turn the wing feed on (in the air).  Air would then rise up (mostly due to more pressure in the main due to a main tank cap tube that produced pressure better) and that higher pressure would push air (in the half empty tank) up into the feed line to the wing and "lock" out the flow.  I'd have to land and blow air into the wing cap tube to restart flow.

So, possibly like the OP here, I was in a situation with unusable fuel in a wing (due to more pressure in one tank than the other). 

Here's a possible scenario that would be like  what I experienced:  If his right tank pressurized better, then it may have fed better and went empty sooner.  Then, when empty, the pressure tube on the right continued to push across to his feeder / header (assuming no vent from header to left tank).  The pressure from the right may have had nowhere to go except up the fuel line to the left, stopping flow similarly to what I experienced.

If you think about it,  it would be possible, (on the ground without header tank venting) to pressurize one empty tank enough to even reverse flow or blow air bubbles across to the other tank (if it were empty enough without a lot of head pressure), and that is why I am in the camp of header tank venting.  But, admittedly, this scenario I purpose only arises in the air with a significant pressure differential (uncommon) and low head pressure (low quantity in other tank).  Kind of a rare scenario, and that is probably why systems without vents work just fine for people most all of the time.

Edited 15 Aug 2018 by Yamma-Fox

[skypics 89]

I have purposely let on of my 14 gallon tanks run dry and did not have an engine stoppage. I have a tube-type header tank where the tanks inputs come together into the header.

Engine failures can happen so if you are interested in practicing engine out landings let me know.

I have a group of pilots who practice accuracy dead stick landings on El Mirage dry lake just south of Edwards AFB where the ultimate dead stick landing from space took place.

We set up cones and markers to measure how close we come to the target cones.

We start with idle only landings and then progress to shutting off the engine on the downwind.

After about three tries we find that pilots can land within 100 feet of the desired touch down spot.

As student pilots, we are trained in engine failures with the engine idling. There is a huge difference with the prop stopped or windmilling as opposed to idling.

All are invited.

Let me know if you are interested and I will include you in my notification list.

I can also give a WINGS presentation to your EAA Chapter titled MIDAIRS AND DEAD STICKS. It is a sancioned WINGS course for 1 credit.

 

John M

 

[NorthIdahoAvidflyer 374]

This is a very interesting thread. I have the same set-up as Jeromef but installed a shut-off on each tank inline before the header. I've often wondered if my header needed to be vented as my tanks do the same thing. My right tank flows faster than my left. I recently flattened out the line coming from from the left tank as it had a flat spot in it. I can turn the right tank off and it drains fine out of the left. I have not flown this much at all so I'm wondering if I need to address something before I do. 

 

[Guest]

If you have a single tank feeding the header it is entirely possible to get an air lock or what ever you want to call it (trapped air in the header that does not/cannot escape). if you have two separate tanks feeding the header, imbalance in the system whether it be sitting on an incline, or uneven fuel draw, or slipping the plane or an uncoordinated turn will all eventually work the air out of the header. 

If for some reason one tank gets drawn down to nothing, what you have then is the equivalent of a single tank with vented header and fuel will "rise" to the head pressure of the system in the "empty" line.

So two fuel tanks feeding a single header tank (with separate connections to the header) is a perfectly viable system. 

This is what I believe anyway. Of course if you have shut off valves for each tank, and you close one and there is air in the header, that air may not be able to escape because now it is a single tank feeding the header with no vent.

[akflyer 1427]

biggest reason I have seen for one tank draining faster than the other is the tendency to fly one wing low or in a slight yaw.  I land and take off on both tanks and have both on when yanking and banking down low.  Normal cruise I will only have the valve open on one tank at a time. 

 

[Jeromef 76]

Update:

Yesterday, I drained the fuel circuit and inspected the "finger strainers"

They were not totally clean (as you would expect for parts which IMHO  were never inspected nor cleaned since the plane was assembled, as they were epoxy sealed) , but in no way clogged or obstructed.

[Turbo 162]

I have only a single tank, but a vent line joins the fuel line at the aluminum-tube header tank behind the right seat.  I always fly with the vent line open, as I use it to reckon fuel quantity.  I have never had air from the vent line enter the header tank, stopping the flow of fuel.  With one tank empty you have essentially the same condition - with one important exception:  Where my lines join down at the header tank, the static head is about 3 ft of fuel, something around 1 psi or a little more.  If your fuel lines from the two tanks join up high, near the tanks, an empty tank may simply suck air, as happened to you, as there is not enough head at the confluence to back-fill the empty line to counter the potential inflow of air, especially in a dynamic situation, where slight differences in pressure drop exist.  Also, you would be susceptible to fuel cutoff in uncoordinated flight, such as, say a slip, with empty wing high, even with a little fuel still in the nearly-empty tank, as it gets used up.  If you run each tank's individual fuel line down to join at the header tank, this problem will go away.  The additional static head will cause the fuel line from the empty tank to almost completely back-fill, blocking the entry of air, and fuel will be drawn from any tank containing fuel.  The only problem with this setup is sensitivity to uncoordinated flight when nearly full, which could cause you to lose fuel.  This is the big advantage of a fuel selector valve. . You won't lose fuel in a slip.  By the way: the speed of the fuel through the lines is only on the order of 10 in/sec at full throttle - pretty slow, and the pressure drop through a clean paper inline fuel filter is negligibly small, way less than a psi. (I just tested this on my Avid with 582!).

Edited 31 Aug 2018 by Turbo

[Jeromef 76]

Turbo

I think you have a good point, the junction of both tank lines is high in my setup.

I ordered 3 fuel valves- one for right tank, one for left and the last for vent line, I will install them this weekend.